Hepatic expression of the scavenger receptor class B type I (SR-BI) promotes selective uptake of HDL cholesterol by the liver and is believed to play a role in the process of reverse cholesterol transport (RCT). We hypothesized that hepatic SR-BI expression is a regulator of the rate of integrated macrophage-to-feces RCT and used an in vivo model to test this hypothesis. Cholesterol-loaded and [³H]cholesterol-labeled J774 macrophages were injected intraperitoneally into mice, after which the appearance of the [³H]cholesterol in the plasma, liver, and feces over 48 hours was quantitated. Mice overexpressing SR-BI in the liver had significantly reduced [³H]cholesterol in the plasma but markedly increased [³H] tracer excretion in the feces over 48 hours. Conversely, mice deficient in SR-BI had significantly increased [³H]cholesterol in the plasma but markedly reduced [³H] tracer excretion in the feces over 48 hours. These studies demonstrate that hepatic SR-BI expression, despite its inverse effects on steady-state plasma HDL cholesterol concentrations, is an important positive regulator of the rate of macrophage RCT.